C Program to Check Co-Prime Numbers

Two numbers are said to be co-prime numbers if they do not have a common factor other than 1 or two numbers whose Highest Common Factor (HCF) or Greatest Common Divisor (GCD) is 1 are known as co-prime numbers.

Examples of co-prime numbers are: 3 and 7 are co-prime, 7 and 10 are co-prime etc.

Note : Co-prime numbers do not require to be prime numbers.

Program

#include<stdio.h>
#include<conio.h>

int main()
{
	 int num1, num2, hcf, i;
	 clrscr();
	 printf("Enter two numbers:\n");
	 scanf("%d%d", &num1, &num2);
	
	 // Finding HCF
	 for(i=1;i<=num1;i++)
	 {
	  if(num1%i==0 && num2%i==0)
	  {
	   hcf = i;
	  }
	 }
	
	 // Making Decision
	 if(hcf == 1)
	 {
	  printf("%d and %d are CO-PRIME NUMBERS.", num1, num2);
	 }
	 else
	 {
	  printf("%d and %d are NOT CO-PRIME NUMBERS.", num1, num2);
	 }
	 getch();
	 return(0);
}

Output of the above program :

Run 1:
-------
Enter two numbers:
13 ↲
10 ↲
13 and 10 are CO-PRIME NUMBERS.

Run 2:
-------
Enter two numbers:
15 ↲
10 ↲
15 and 10 are NOT CO-PRIME NUMBERS.

Note: ↲ indicates enter is pressed.